Reliability testing of frequency converters with salt spray and temperature humidity tests

In this study an accelerated corrosion test was developed for a frequency converter with markedly high reliability. Constant humidity and salt spray testing were used, as they are commonly used methods for accelerated corrosion testing. The purpose of the test was to study the persistence of the device against corroding atmosphere and to examine failure locations and mechanisms. Testing included 24 hour exposure to neutral salt spray in accordance with ISO 9227, after which the excess salt residues were removed with deionized water. This was followed by a 24 hour drying period at 23degC and 50%RH. After drying the functionality of frequency converters was tested. The corrosion effect was then precipitated by placing the devices in 85degC and 85 %RH temperature and humidity test for 500 hours. The aforementioned drying period was then repeated before final functional testing. The functional testing was performed by running the frequency converters with overvoltage in a test rig. In order to study the effect of the salt spray, another eight converters were tested using only the 85degC and 85%RH temperature and humidity test. No failures were seen in these converters during the test. However, five of the converters exposed to the salt spray failed during or after the test. Using salt spray testing, quick results could be obtained, as normally the test times required to fail the frequency converter can be very long. The interface between the printed circuit board and the power module of the device was noticed to be the most susceptible to corrosion damage.